1. Field of the Invention
The present invention relates to a method and machine for tamping ballast under a track in a track section delimited by two undercarriages.
2. Description of the Prior Art
British patent No. 2,151,675 discloses a tamping machine comprising a main frame having opposite ends supported on undercarriages delimiting a track section which is lifted and tamped. A longitudinally displaceable satellite frame is arranged between the undercarriages, and the satellite frame is equipped with a track tamping unit and a track leveling and lining unit. The tamping machine advances continuously along the track during a track rehabilitation operation while the displaceable satellite frame moves intermittently for tamping the ballast under the successive ties of the track in the track section.
U.S. Pat. No. 4,644,868 also discloses such a continuously advancing track leveling, lining and tamping machine. One end of the satellite frame is supported by an undercarriage on the track, and the track is lifted and the ballast is tamped in a track section delimited by one of the undercarriages supporting the main frame on the track and the undercarriage supporting the one satellite frame end on the track.
Finally, U.S. Pat. No. 4,794,862 discloses a track tamping machine which comprises a chute for discharging ballast in the track section being lifted and tamped. This optimizes the track correction operation by providing sufficient ballast to assure a long-lasting corrected track position.
It is the primary object of this invention to improve track tamping by permitting newly delivered ballast to be tamped rapidly and efficiently under the ties of a track.
It is another object of the invention to provide a track tamping machine which is alternately usable for optimal tamping of newly delivered ballast and a normal tamping operation.
The above and other objects of the present invention are accomplished according to one aspect of this invention with a method of tamping ballast under a track in a track section delimited by two undercarriages, which comprises the steps of extending the length of the track section in a first operating stage during which ballast is delivered to the track while the track is lifted, and shortening the track section in a second operating stage during which the ballast is tamped until a desired track level has been obtained.
Lifting of the track section to a higher level is possible by extending the length of the track section without subjecting the track rails to undue stress as they are bent during lifting. This higher track lift has the advantage that a substantial amount of ballast may be delivered in a single operating stage for tamping under the ties of the track, particularly in connection with a new ballasting of the track. As soon as all the required ballast has been disposed under the track, the track section may be shortened in a second operating stage to obtain a desired track level and tamp the ballast under the ties for achieving a durable corrected track position.
According to another aspect of the invention, there is provided a mobile machine for tamping ballast under a track, which comprises a main frame extending in a longitudinal direction and having opposite ends supported on the track by two undercarriages, and a satellite frame arranged between the two under carriages and having opposite ends, one of the satellite frame ends having a link connecting the one satellite frame end to the main frame for displacement in the longitudinal direction, the opposite satellite frame end having another undercarriage for support on the track, and the satellite frame carrying a tamping unit and a track leveling and lining unit. A lifting drive connects the opposite satellite frame end to the main frame, and guide rollers are connected to the lifting drive for moving the lifting drive in the longitudinal direction.
Providing the lifting drive movable on the guide rollers in the longitudinal direction enables the length of the track section to be adjusted simply by actuating the lifting drive and without requiring additional work. The high efficiency of a continuously advancing track tamping machine remains unimpaired in both operating stages.